1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to dimple patterns of golf balls.
2. Description of the Related Art
Golf balls have numerous dimples provided on the surface thereof. A role of the dimples involves causing turbulent flow detachment through disrupting the air flow around the golf ball during the flight (hereinafter, referred to as “dimple effect”). By causing the turbulent flow detachment, a detachment point of air from the golf ball shifts backwards leading to the reduction of a drag coefficient (Cd). The turbulent flow detachment promotes the difference of positions of the upper detachment point and the lower detachment point resulting from the back spin, thereby enhancing the lift force that acts upon the golf ball. Flight distance of the golf ball is prolonged on behalf of reduced drag and improvement of lift force. Aerodynamically excellent dimples promote the turbulent flow detachment. In other words, aerodynamically excellent dimples may render the air flow better.
For the arrangement of dimples, a polyhedron (in particular, regular polyhedron or semiregular polyhedron) is often employed. When a polyhedron is employed, a polyhedron inscribed in a phantom spherical face is envisioned, and comparting lines are formed by casting a reflection of sides of the polyhedron with a beam of light radiated from the center of the sphere onto the phantom spherical face. The phantom spherical face is comparted with these comparting lines, and the dimples are arranged accordingly. Examples of the regular polyhedron which may be employed include the regular hexahedron, regular octahedron, regular dodecahedron and regular icosahedron. In addition, illustrative examples of the semiregular polyhedron which may be employed include the icosidodecahedron and cuboctahedron. A dimple pattern arranged employing the icosidodecahedron is disclosed in JP-A No. 60-234674. A dimple pattern arranged employing the cuboctahedron is disclosed in JP-A No. 1-221182.
Various arts for improving the flight performance of a golf ball by modifying the plane shape of dimples have been proposed. For example, JP-A No. 4-220271 discloses a golf ball with adjacent two types of dimples having the different shape. JP-A No. 5-84328 discloses a golf ball provided with circular dimples and noncircular dimples. JP-A No. 5-96026 discloses a golf ball provided with dimples which are noncircular and have their sectional form with double slope. Persons skilled in the art are aware of great dimple effect achieved by noncircular dimples. Dimple effect of polygonal dimples is particularly great. Golf balls provided with polygonal dimples are excellent in flight performance.
In light of the improvement of appearance and the improvement of surface area occupation percentage of a golf ball, it is preferred that numerous polygonal dimples are arranged in an orderly array. Polygonal dimples have insufficient symmetry compared to circular dimples. When such polygonal dimples are arranged in an orderly array, there is the possibility that aerodynamic symmetry as a golf ball is impaired. An object of the present invention is to provide a golf ball which is excellent in flight performance and aerodynamic symmetry.